Aluminum-shielded coaxial cable is commonly used in aerial installations where it is supported on poles. Due to the high thermal expansion coefficient of aluminum, expansion loops are used in such installations to ease the tension exerted on splices, tap boxes, junctions, and other equipment to which the coaxial cable is connected. Cracks frequently develop in the aluminum shielding due to a number of reasons, including repeated flexing and work hardening of the aluminum, defects in the manufacture of the aluminum shielding, and incorrect handling or installation of the aluminum-shielded coaxial cable.
When cracks or other openings occur in the aluminum shielding, a number of problems result, which include radio frequency (RF) interference passing through the shielding in both directions, which cause interference with the signals carried by the cable when radio frequencies enter through the opening in the aluminum shield and interference with other transmitted signals when the signal carried by the cable leaks out of the cable through the opening in the aluminum shield. The opening in the aluminum shield also allows moisture to enter which causes corrosion and interferes with the dielectric properties of the insulation between the outer conductor aluminum shielding and the center conductor of the cable.
Aluminum-shielded coaxial cable is difficult to repair because of the properties of the aluminum, including the oxidation layer on the aluminum, the corrosion tendencies of aluminum and the cold flow or stress relaxation of the aluminum. In order to properly repair a crack in the aluminum shield, the opening must be electrically-shielded to prevent radio frequency interference in and out of the cable and it must be environmentally sealed to prevent moisture from entering the cable. The methods conventionally used to repair the cables include cutting the cable to remove the portion of the cable containing the crack in the shield and splicing the cable together using a splice connector. This method has the disadvantages of requiring an interruption of the service carried by the cable and in those cases where insufficient cable length is available, an additional length of cable must be supplied, thus requiring two splice connectors. Another method involves the use of a conductive tape to wrap the aluminum jacket of the cable, such as disclosed in U.S. Pat. No. 4,283,238. This method has the disadvantage of being efficient in establishing the radio frequency shielding because of the oxide layer on the surface of the aluminum interfering with the electrical contact between the aluminum shield and the conductive tape.